Author(s)

R. TANTRA, D. GOHIL, S. KALIYAPPAN & S. JING

Abstract

There is a great deal of concern about the safety of nanoparticles and their effect on the environment; this has led to a recent Organisation for Economic Co-operation and Development (OECD) drive for testing the toxicity of industrially relevant nanomaterials. A fundamental aspect of the research is the need to measure particle size and particle concentration accurately and reliably, as these two parameters will infl uence toxicity. The current paper presents a study that aims to characterise CeO2 nanoparticles for the purpose of ecotoxicological studies, and this has resulted in a two-part study that is presented in this paper. The aim of the fi rst part of the study was to observe if small nanosized clusters (<1 μm) existed when dispersed in four ecotoxicological media (i.e. fi sh, daphnia, seawater and de-ionised water); this was done qualitatively using Scanning Electron Microscopy. The second part of the study aimed to explore the feasibility of Nanoparticle Tracking Analysis (NTA) as a suit-able tool to characterise not only particle size but also particle number concentration. This involved dispersing CeO2 in DI water and diluting the stock solution into nine different concentrations. Particle size and number data were then acquired using NTA; particle size data were compared to the corresponding Dynamic Light Scattering (DLS) response. The results were as follows: (a) although the majority of the nanomaterials were large aggregates (at least few microns in dimensions), smaller clusters (<800 nm) were shown to be present in all four media; it is the fate of these small size clusters that should be monitored if hypothesis relating toxicity to particle size holds true, (b) as a tool NTA yielded small particle size compared to DLS measurements and the limit of quantifi cation is shown to be >0.1 mg/L, as NTA tracks individual particles and does not suffer limitations observed with DLS, in which larger particles can potentially mask signal of smaller particles and (c) calibration curve for number concentration by NTA did not yield a linear response; the non-linear response observed should be further investigated if NTA is going to be used to measure particle number concentration, particularly in the low concentration range.

Keywords

Agglomerates, aggregation, aquatic ecotoxicity, CeO2, characterisation, dispersion, DLS, nanoparticles, NTA, SEM